Thermal event management system for an electric vehicle

ABSTRACT

A method of controlling the battery system of an electric vehicle includes detecting a thermal event in a first battery pack of a plurality of battery packs of the battery system, and at least partially powering down the electric vehicle automatically in response to the detected thermal event. The method may also include initiating a thermal rejection scheme in response to the detected thermal event.

TECHNICAL FIELD

Embodiments of this disclosure relate to thermal event managementsystems for an electric vehicle.

BACKGROUND

An electric vehicle (EV) uses an electric motor for propulsion. Energyrequired to power the propulsion motor is stored in a battery systemlocated in the vehicle. In many EV applications, lithium ion batterycells are used in their battery systems. It is known that defects inlithium ion battery cells may lead to an unexpected increase in celltemperature. In some cases, the increase in cell temperature may lead toan undesirable thermal event (such as, for e.g., thermal runaway) in thebattery system. Embodiments of the current disclosure provide systemsand methods to reduce the occurrence or severity of such thermal events.The scope of the current disclosure, however, is defined by the attachedclaims, and not by the ability to solve any specific problem.

SUMMARY

Embodiments of the present disclosure relate to a thermal eventmanagement system of an electric vehicle. Each of the embodimentsdisclosed herein may include one or more of the features described inconnection with any of the other disclosed embodiments.

In one embodiment, a method of controlling the battery system of anelectric vehicle is disclosed. The battery system includes a pluralityof battery packs, and each battery pack includes multiple battery cellselectrically coupled together. The method may include detecting athermal event in a first battery pack of the plurality of battery packsusing an electronic controller of the electric vehicle, and at leastpartially powering down the electric vehicle automatically in responseto the detected thermal event. The method may also include initiating athermal rejection scheme in response to the detected thermal event.

In another embodiment, a method of controlling the battery system of anelectric vehicle is disclosed. The battery system includes a pluralityof battery packs, and each battery pack includes multiple battery cellselectrically coupled together. The method may include receiving, at anelectronic controller, data from one or more sensors coupled to eachbattery pack of the plurality of battery packs. The method may alsoinclude detecting, based on the received data, a thermal event in afirst battery pack of the plurality battery packs, and electricallydecoupling the first battery pack from the battery system in response tothe detecting. The method may further include increasing a rate ofcooling of the first battery pack relative to the rate of cooling of asecond battery pack of the battery system in response to the detecting.

In yet another embodiment, a method of controlling the battery system ofan electric vehicle is disclosed. The battery system includes aplurality of battery packs, and each battery pack includes multiplebattery cells electrically coupled together. The method may includedetecting, based on data received from one or more sensors coupled toeach battery pack of the plurality of battery packs, a thermal event ina first battery pack of the plurality of battery packs. The method mayalso include sending information regarding the detected thermal event toan operator of the electric bus, and turning off substantially all powerfrom the battery system after a predetermined amount of time afterdetecting the thermal event. The method may further include increasing arate of cooling of the first battery pack relative to the rate ofcooling of a second battery pack of the plurality of battery packs inresponse to the detecting.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate exemplary embodiments of thepresent disclosure and together with the description, serve to explainthe principles of the disclosure.

FIG. 1 illustrates an exemplary electric bus having a battery system;

FIG. 2 is a schematic illustration of an exemplary battery system of thebus of FIG. 1;

FIG. 3 is a schematic illustration of an exemplary battery pack of thebattery system of FIG. 2; and

FIG. 4 is a flow chart of an exemplary method of managing a thermalevent in the bus of FIG. 1.

DETAILED DESCRIPTION

The present disclosure describes a thermal event management system of anelectric vehicle. While principles of the current disclosure aredescribed with reference to an electric bus, it should be understoodthat the disclosure is not limited thereto. Rather, the systems andmethods of the present disclosure may be used in any application(electric vehicle, electric machine, electric tool, electric appliance,etc.). In this disclosure, relative terms, such as “about,”“substantially,” or “approximately” are used to indicate a possiblevariation of ±10% of a stated value.

FIG. 1 is a bottom view of exemplary low-floor electric bus 10. As isknown in the art, a low-floor bus is a bus with its floor positionedclose to the road surface (e.g., 12-16 inches or 30-40 centimeters) toease passenger entry and exit. Electric bus 10 may include a body 12enclosing a space for passengers. In some embodiments, the body 12 maybe fabricated using composite materials to reduce the weight of the bus10. One or more electric motors 16 generate power for propulsion of thebus 10, and a battery system 14 stores the electrical energy needed topower the motor(s) 16. When the energy stored in the battery system 14decreases, it is recharged using power from an external energy source(e.g., utility grid, a bank of batteries, etc.). The battery system 14may be recharged by any method. Commonly-assigned U.S. PatentApplication Publication Nos. US 2013/0193918 A1 and US 2014/0070767 A1,and U.S. patent application Ser. No. 15/227,163, filed Aug. 3, 2016,which are incorporated by reference in their entirety herein, describeexemplary methods for recharging the battery system 14.

FIG. 2 is a schematic illustration of an exemplary battery system 14 ofbus 10. Battery system 14 may include any type of vehicle battery knownin the art. In some embodiments, the battery system 14 may have amodular structure and may be configured as a plurality of battery packs20 electrically connected together. In general, the battery packs 20 maybe positioned anywhere on bus 10 (inside, outside, roof, etc.). In someembodiments, as illustrated in FIG. 1, the battery packs 20 arepositioned under the floor of the bus 10. Since the battery system 14may have considerable weight, positioning the battery packs 20 under thefloor may assist in lowering the center of gravity of the bus 10 andbalance its weight distribution, thus increasing drivability and safety.Each battery pack 20 includes components (described later) enclosed in aprotective housing 24. In general, the battery system 14 may include anynumber of battery packs 20. These battery packs 20 may be connectedtogether in any manner (series, parallel, or a combination of both). Insome embodiments, the battery packs 20 may be arranged in strings. Forexample, multiple strings of battery packs 20 may be connected inparallel, with each string including a plurality of battery packs 20connected together in series. Configuring the battery system 14 asparallel-connected strings allows the bus 10 to continue operating withone or more strings disconnected if a battery pack 20 in a string fails.However, in some embodiments, all the battery packs 20 of a batterysystem 14 may be connected in series or parallel.

Referring to FIG. 2, a battery management system (BMS 60) controls theoperations (related to charging, discharging, thermal management, etc.)of the battery system 14. The BMS 60 may include circuit boards,electronic components, sensors, and controllers that monitor theperformance of the components of the battery system 14 based on sensorinput (e.g., voltage, current, temperature, humidity, pressure, etc.),provide feedback (alarms, alerts, etc.), and control the operation ofthe battery system 14 for safe and efficient operation of the bus 10.Among other functions, as will be described in more detail later, BMS 60may thermally and/or electrically isolate portions of the battery system14 when one or more sensor readings indicate defects in portions of thebattery system 14. An exemplary BMS 60 that may be used in batterysystem 14 is described in commonly-assigned U.S. Patent ApplicationPublication No. US 2012/0105001 A1, which is incorporated by referencein its entirety herein.

Battery system 14 includes a thermal management (TM) system 40 (e.g.,heating and/or cooling system) to manage the temperature of the batterypacks 20 within acceptable limits. The TM system 40 may include conduits18 that direct a TM medium 8 (e.g., coolant, etc.) to the differentbattery packs 20 of the battery system 14. Although not illustrated, acoolant pump may circulate the TM medium 8 through the battery system14. In some embodiments, the TM medium 8 circulating through theconduits 18 may be a liquid coolant that is used to heat/cool othercomponents of the bus 10. One or more control valves 22 may be fluidlycoupled to the conduits 18 and configured to selectively direct the TMmedium 8 to one or more desired battery packs 20 of the battery system14. For example, based on sensor inputs (indicative of the temperature,etc.) from a battery pack 20, the BMS 60 (or another controller) mayactivate the valves 22 to redirect the TM medium 8 to a battery pack 20to increase or decrease its temperature.

FIG. 3 is a schematic illustration of an exemplary battery pack 20 ofbattery system 14. As illustrated in FIG. 3, the battery pack 20includes a plurality of battery modules 30 enclosed within its housing24. The housing 24 of the battery pack 20 encloses the plurality ofbattery modules 30 such that these modules 30 are physically isolated,and walled off, from other modules 30 of the battery system 14. Thus,the housing 24 of each battery pack 20 may contain the damage resultingfrom a catastrophic high temperature event (such as, for example,overheating, arcing, fire, etc.) of a battery module 30 within thebattery pack 20, and delay (or prevent) its spreading to other batterypacks 20. The housing 24 also assists in focusing additional cooling (aswill be described later) to the affected modules 30 to mitigate theseverity of the failure. In some embodiments, the battery modules 30 ofa battery pack 20 may be separated from each other with dividers (notshown), to protect other battery modules 30 from a battery module 30experiencing a failure.

The housing 24 and the dividers may be made of a material that does notoxidize or otherwise become damaged when exposed to electrical arcsand/or high temperatures. In some embodiments, the housing 24 may beconstructed of high strength, corrosion resistant, and/or punctureresistant materials (e.g., composite materials, Kevlar, stainless steel,aluminum, high strength plastics, etc.). Although not a requirement, insome embodiments, the housing 24 may have a box-like structure and/ormay be shaped to allow the battery modules 30 (of the battery pack 20)to be arranged in a single layer to decrease the height of the batterypack 20 (e.g., so that they can be fit under the floor of a low-floorbus). In some embodiments, the housing 24 may be watertight (e.g., toapproximately 1 meter) and have an International Protection (IP) 67rating for dust and water resistance.

As illustrated on the top right battery module 30 of FIG. 3, eachbattery module 30 includes a plurality of battery cells 50 packagedtogether within a casing 32. Similar to housing 24 of a battery pack 20,casing 32 may be configured to contain any failures (electric arcs,fires, etc.) of the cells 50 of the module 30 within the casing 32 anddelay the damage from spreading to other modules 30 of the battery pack20. Casing 32 may be made of any material suitable for this purpose(e.g., Kevlar, aluminum, stainless steel, composites, etc.) In general,the cells 50 may have any shape and structure (cylindrical cell,prismatic cell, pouch cell, etc.). In addition to the cells 50, thecasing 32 may also include sensors (e.g., temperature sensor, voltagesensor, humidity sensor, etc.) and controllers that monitor and controlthe operation of the cells 50. Although not illustrated, casing 32 alsoincludes electrical circuits (voltage and current sense lines, lowvoltage lines, high voltage lines, etc.), and related accessories(fuses, switches, etc.), that direct electrical current to and from thecells 50 during recharging and discharging.

As known in the art, each battery cell 50 is a unit that comprises twoelectrodes (anode and a cathode) with an electrolyte (a chemical)between them. Although not a requirement, in some embodiments, theelectrolyte may have a lithium-ion chemistry (e.g.,lithium-nickel-cobalt-aluminum (NCA), lithium-nickel-manganese-cobalt(NMC), lithium-manganese-spinel (LMO), lithium titanate (LTO),lithium-iron phosphate (LFP), lithium-cobalt oxide (LCO), etc.).Simplistically, when the two electrodes of the cell 50 are connected ina circuit, the chemical energy of the electrolyte is converted toelectrical energy. Thus, each battery cell 50 is the smallestself-contained unit that converts chemical energy to electrical energy.

Each battery module 30 is formed by connecting together multiple cells50 and encasing them in a casing 32, and each battery pack 20 is formedby connecting together multiple modules 30 and encasing them in ahousing 24. Although not a requirement, the battery packs 20 of thebattery system 14 may be substantially identical to each other (e.g., interms of number of modules 30, number of cells 50 in each module 30, howthe modules 30 and cells 50 are electrically connected together, etc.).Although the battery system 14 of FIG. 2 is illustrated as having sixbattery packs 20, and the battery pack 20 of FIG. 3 is illustrated ashaving six battery modules 30, this is only exemplary. Battery system 14may have any number of battery packs 20, each battery pack 20 may haveany number of battery modules 30, and each battery module 30 may haveany number of battery cells 50. In some embodiments, the number ofbattery packs 20 in the battery system 14 may be between about 2-6, thenumber of battery modules 30 in each battery pack 20 may be between10-20, and the number of battery cells 50 in each battery module 30 maybe between about 400-700.

The battery modules 30 of each battery pack 20, and the battery cells 50of each battery module 30, may be electrically connected together inseries, parallel, or a combination of series and parallel. In someembodiments, some of the battery modules 30 in a battery pack 20 may beconnected together in series, and the series-connected modules 30connected together in parallel. Similarly, in some embodiments, a groupof battery cells 50 of each module 30 may be connected together inseries to form multiple series-connected groups of cells 50, and theseseries-connected groups may be connected together in parallel. However,in some embodiments, all the battery modules 30 of a battery pack 20,and all the battery cells 50 of a battery module 30, may be connectedtogether in series or parallel.

In addition to the battery modules 30, the housing 24 of each batterypack 20 may also enclose other components that aid in the functioning ofthe battery pack 20. These components may include a plurality of sensors34 a, 34 b, 34 c, 34 d that monitor different operating parameters(e.g., current, voltage, etc.) and ambient conditions (temperature,humidity, pressure, etc.) of the battery pack 20. For example, atemperature sensor 34 a (e.g., thermistor) may monitor the temperaturein the battery pack 20, a humidity sensor 34 b may monitor the humidityin the battery pack 20, a pressure sensor 34 c may monitor the pressurein the battery pack 20, and a current/voltage sensor 34 d may monitorthe current/voltage directed into or out of the battery pack 20. In someembodiments, multiple temperature, humidity, pressure, and/or currentsensors may be provided at different locations of the battery pack 20.These multiple sensors may be used to monitor the conditions indifferent regions of the battery pack 20. In some embodiments, one ormore temperature, humidity, pressure, and current/voltage sensors 34 a,34 b, 34 c, 34 d may also be provided within every battery module 30 ofthe battery pack 20 to monitor the conditions in each battery module 30(or in different regions of the battery module 30). Each battery pack 20may also include a pack controller 26 that cooperates with the BMS 60 tocontrol the operation of the battery modules 30 based on input from thesensors (e.g., sensors 34 a, 34 b, 34 c, 34 d).

The conduits 18 of the TM system 40 may extend into the battery pack 20through the housing 24. The conduits 18 may also extend into each module30 of the battery pack 20 through its casing 32. As illustrated in FIG.3, these conduits 18 may circulate the TM medium 8 through the batterypack 20 and through its multiple modules 30 for thermal management(e.g., heat or cool) of the modules 30. The TM medium 8 passing througheach module 30 may be used to control the temperature of the cells 50 inthe module 30 within acceptable limits. Although not illustrated in FIG.3, in some embodiments, valves may also be fluidly coupled to theseconduits 18 (e.g., as illustrated in FIG. 2) to selectively direct theTM medium 8 to any desired battery module 30 (e.g., in response toinstructions from the pack controller 26 and/or the BMS 60). Forexample, based on a detected high temperature in a module 30, the packcontroller 26 may redirect the TM medium 8 from other modules 30 to theaffected module 30 to quickly decrease its temperature. In someembodiments, a TM element 28 (e.g., heater, heat exchanger, chiller,etc.) may also be fluidly coupled to the conduits 18 to heat or cool theTM medium 8. Although not illustrated, in some embodiments, the housing24 of the battery pack 20 may also include vents, ducts, valves, andother features/components (e.g., fans) to circulate air or another gasthrough the battery pack 20.

During operation of the battery system 14 (i.e., during charging,discharging, etc.), the battery cells 50 generate heat due to thechemical reactions that occur in these cells. The heat generated by thecells 50 increase the temperature of the battery modules 30. The TMmedium 8 (and/or the air) circulating through the battery pack 20 andits modules 30 may remove a portion of the heat to maintain the cells 50at an acceptable temperature. The BMS 60 (alone or along with othercontrollers such as pack controller 26) may monitor the temperature ofthe battery pack 20 and its modules 30 (based, for example, on inputfrom temperature sensors 34 a), and increase the rate of cooling of thebattery pack 20 if the monitored temperature exceeds a preprogrammedthreshold value. The rate of cooling may be increased by any method. Insome embodiments, the flow rate of the TM medium 8 through the batterypack 20 (or a specific module 30 in the pack 20) may be increased toincrease the rate of cooling.

As is known in the art, in some cases, some of the battery cells 50 ofthe battery system 14 may experience an unexpected thermal event (e.g.,a thermal runaway) resulting in an uncontrolled increase in temperatureof the affected battery cells 50. Since the battery cells 50 are inclose proximity to each other, if left unchecked, thermal runaway thatbegins in a few cells 50 can start a chain reaction that spreads to thesurrounding cells 50, modules 30, and packs 20. BMS 60 may include amethod that detects such thermal events at an early stage and takesremedial action. As described in more detail below, the remedial actionmay include, among other actions, initiating a thermal rejection schemeto reduce the severity of the thermal event, gracefully powering downthe bus 10, and assisting the driver in safely evacuating passengersfrom the bus 10.

FIG. 4 is a flow chart that illustrates an exemplary method 100 used bythe BMS 60 to detect a thermal event and take remedial action. In thedescription below, reference will also be made to FIGS. 2 and 3. Themethod 100 includes detecting a thermal event in the battery pack (step110). BMS 60 may detect the thermal event based on signals from one ormore of the sensors (e.g., temperature sensor 34 a, humidity sensor 34b, pressure sensor 34 c, and current/voltage sensor 34 d) embedded in abattery module 30 (or a battery pack 20) of the battery system 14. Insome embodiments, readings from one or more of these sensors that exceeda threshold value may indicate a thermal event. In some embodiments, areading from one sensor in a module 30 (or a pack 20) relative to thereading from another sensor may indicate the occurrence of a thermalevent. For example, a temperature or humidity reading from a firstsensor in a module 30 that is significantly higher than a correspondingreading from a similarly situated second sensor may indicate theoccurrence of a thermal event proximate the first sensor. In someembodiments, a combination of signals from several sensors in a module30 (or a pack 20) may indicate the occurrence of a thermal event.

In some embodiments, the BMS 60 may detect a thermal event in a batterymodule 30 based on a pressure signal. For example, when battery cells 50experience a thermal event, a gas is released (or vented) from theaffected cells 50. The released gas increases the pressure within thebattery module 30 or battery pack 20. This increase in pressure isdetected by a pressure sensor 34 c positioned in the module 30 orbattery pack 30. BMS 60 may be configured to recognize the observedpressure signal (magnitude, rate of change, etc.) as one that resultsfrom a thermal event in the module 30. In some embodiments, a humiditysensor 34 b in the module 30 may detect an increase in humidityresulting from the gas released by an affected cell 50, and the BMS 60may detect a thermal event based on a signal from the humidity sensor 34b.

A thermal event in a module 30 may also be detected by BMS 60 usingisolation resistance monitoring. For example, the gas released from anaffected cell 50 may be conductive, and the presence of the gas in abattery pack 20 may decrease the isolation resistance between the highvoltage system and the low voltage system of the battery pack 20. TheBMS 60 may monitor this resistance (for example, using a voltage/currentsensor connected between the low and high voltage systems) and detectthe occurrence of a thermal event based on the monitored isolationresistance. In some embodiments, a combination of some or all of apressure signal, a humidity signal, and isolation resistance monitoringmay be used to detect the presence of discharged gas in a battery pack20 (or battery module 30). Detecting a thermal event based by detectingthe gas discharged from a battery cell 50 may enable the thermal eventto be detected closer to its onset.

In some embodiments, the BMS 60 may detect a thermal event in a module30 based on a signal from the temperature sensor 34 a in the module 30.For example, a temperature recorded by a temperature sensor 34 a, or therate of temperature increase recorded by one temperature sensor 34 a (ina module 30 or a pack 20) relative to other temperature sensors 34 a (inthe same module 30 or pack 20) may be indicative of a thermal event. Insome embodiments, BMS 60 may detect the onset or the existence of athermal event based on a combination of readings from multiple sensors(temperature sensor 34 a, humidity sensor 34 b, pressure sensor 34 c,etc.).

When a thermal event is detected in the battery system 14, the BMS 60may inform the driver and/or other relevant authorities (e.g., servicepersonnel, bus operator, etc.) of the thermal event (step 120).Informing the driver may include one or more of sounding an audio alarm,activating one or more indicator lights, and/or displaying messages onthe bus display system (e.g., a display screen positioned in view of thedriver within the bus 10). These messages may include, among others,information about the location of the thermal event, and instructions topull the bus 10 over (if the bus 10 is in motion) and begin anevacuation process. Bus 10 has several doors/hatches that a passengermay use to exit the bus 10 (e.g., front door, rear door, roof hatch,etc.). The messages to the driver may include suggestions to evacuatethe bus 10 using a particular exit based on where the thermal event isoccurring. For example, if the BMS 60 detects that the thermal event isoccurring in a battery pack 20 positioned towards the front of the bus10, the BMS 60 may instruct the driver to evacuate the bus 10 using therear door. In some embodiments, the BMS 60 may also automatically openthe suggested exit door (and or other doors and windows), and/oractivate other systems of the bus 10 (e.g., lights, etc.) to speed theevacuation process. In some embodiments, alternate to, or in additionto, the displayed messages, the BMS 60 may also provide verbalinstructions to the driver and passengers over an audio system of thebus 10. The BMS 60 may also automatically contact and report (e.g.,wirelessly) the detected thermal event to service personnel (and/orother authorities) so that they can quickly respond to the disabled bus10.

Upon detection of a thermal event, the BMS 60 may also power down thebus 10 (step 130). The bus 10 may be powered down in a manner that givesthe driver enough time to stop the bus 10 at a suitable location, andthe passengers enough time to exit the bus 10. For example, in someembodiments, upon detection of a thermal event in a battery module 30 ofa battery pack 20, the BMS 60 may immediately (or after a predeterminedamount of time) electrically decouple (e.g., by opening contactors) theaffected battery pack 20 from the electrical system of the bus 10, andderate the power supplied to the bus 10. Power to various systems of thebus 10 (HVAC, powertrain, etc.) may then be sequentially terminated(e.g., after predetermined amounts of time), such that the bus 10 isslowly and gracefully powered off. That is, substantially all the powerfrom the battery system 14 may be turned off after a finite (non-zero)and predetermined amount of time after detecting the thermal event (step110). In some embodiments, as the various systems are progressivelypowered down, additional battery packs 20 may be decoupled from theelectrical system. The driver may be alerted (e.g., by displayed orannounced messages, etc.) prior to powering down each system. In someembodiments, the driver may be able to override the BMS 60 and delay thepowering down of any particular system (e.g., propulsion system, etc.)to increase the time available to stop and/or evacuate the bus. Poweringdown the bus 10 in this manner may enable the passengers to be safelyevacuated while minimizing damage to the bus 10 and the environment.

The BMS 60 may also initiate a thermal rejection scheme whichaccelerates the removal of heat from the affected module 30 (or pack 20)upon detection of a thermal event in the battery system 14 (step 140).In some embodiments, the thermal rejection scheme may include increasingthe rate of flow of the TM medium 8 to an affected battery module 30when a thermal event is detected in the module 30. For example, when thesensors embedded in a battery module 30 indicates that a thermal eventis occurring in a battery module 30 of a battery pack 20, the BMS 60 maycontrol the coolant pump (fluidly coupled to the conduits 18) toincrease the flow rate of the TM medium 8 in the battery system 14. Insome embodiments, the TM medium 8 flowing through other battery packs 20of the battery system 14 may be redirected (e.g., by selectively closingand opening valves 22) to the affected battery pack 20 to increase heatrejection from the affected battery pack 20, and thereby, quench orminimize the effects of the detected thermal event. In some embodiments,fluid valves in the affected battery pack 20 may also be adjusted (e.g.,opened, closed, etc.) to increase the flow of the TM medium 8 throughthe affected module 30 and increase heat rejection from the module 30.

Alternatively or additionally, in some embodiments, the BMS 60 maycontrol a chiller (or heat exchanger) in TM element 28 to cool the TMmedium 8 in an affected battery pack 20 to increase TM rejection fromthe battery pack 20. For example, when a thermal event is detected in abattery pack 20, the BMS 60 may increase the flow of the TM medium 8into the affected battery pack 20 and activate the chiller to cool theTM medium 8 entering the affected battery pack 20. In some embodiments,a blast of air, fire retardant, or another suitable fluid (e.g., carbondioxide, halon, etc.) may be directed into an affected battery pack 20in response to the detection of a thermal event in the battery pack 20.For example, battery system 14 may include ducting (with valves) thatfluidly couples a canister containing a gas (or a fluid) with theplurality of battery packs 20 of the battery system 14. And, when athermal event is detected in a battery pack 20, the BMS 60 may activatethe flow of the gas from the canister, and control the valves coupled tothe ducting, to direct the gas into the affected battery pack 20 tominimize the severity of the detected thermal event. In someembodiments, an onboard compressor on the bus 10 (e.g., of the airsuspension system or the braking system) may act as a primary or asecondary power source for moving the gas through the affected batterypack 20.

In some embodiments, the thermal rejection scheme employed by the BMS 60in response to a detected thermal event may depend upon the gravity ofthe detected event. For example, in an embodiment of the method, thethermal rejection schemes employed by the BMS 60 may include: (a)controlling the coolant pump to increase the flow rate of the TM medium8 into the battery system 14; (b) redirecting the TM medium 8 from allbattery packs 20 to the affected battery pack 20 by controlling thevalves; (c) activating the chiller in the affected battery pack to coolthe TM medium 8; and (d) directing a burst of a fire retardant into theaffected battery pack 20. And, based on the severity of the detectedthermal event (judged, for example, based on one or more sensorreadings), the BMS 60 may select one or a combination of these schemes(e.g., only (a), a combination of (a), (b), (c), (d), etc.) to employ torespond to the thermal event.

Although FIG. 4, illustrates the different steps of the method 100 asbeing performed in a serial manner, this is only exemplary. In someembodiments, the different steps may be performed simultaneously (or inparallel). For example, upon detection of the thermal event (i.e., step110), the BMS 60 may simultaneously inform the driver (step 120), startthe power down process (step 130), and initiate the thermal rejectionscheme (140). It should also be noted that, although the BMS 60 isdescribed as performing the steps of the described method 100, this isonly exemplary. In general, any controller (or collection ofcontrollers) of the bus 10 may some or all the steps of the method.Additionally, although the method 100 is described with reference to thebattery system 14 of the bus 10, this is only exemplary. In general, themethod may be applied to mitigate a detected thermal event anywhere onthe bus 10.

While principles of the present disclosure are described herein withreference to the battery system of an electric bus, it should beunderstood that the disclosure is not limited thereto. Rather, thesystems described herein may be employed in the batteries of anyapplication. Also, those having ordinary skill in the art and access tothe teachings provided herein will recognize additional modifications,applications, embodiments, and substitution of equivalents all fallwithin the scope of the embodiments described herein. Accordingly, thedisclosure is not to be considered as limited by the foregoingdescription. For example, while certain features have been described inconnection with various embodiments, it is to be understood that anyfeature described in conjunction with any embodiment disclosed hereinmay be used with any other embodiment disclosed herein.

We claim:
 1. A method of controlling the battery system of an electricvehicle, the battery system including a plurality of battery packs, eachbattery pack including multiple battery cells electrically coupledtogether, comprising: detecting a thermal event in a first battery packof the plurality of battery packs using an electronic controller of theelectric vehicle; at least partially powering down the electric vehicleautomatically in response to the detected thermal event; and initiatinga thermal rejection scheme in response to the detected thermal event. 2.The method of claim 1, wherein initiating a thermal rejection schemeincludes increasing a rate of cooling of the first battery pack relativeto the rate of cooling of a second battery pack of the plurality ofbattery packs.
 3. The method of claim 2, wherein increasing the rate ofcooling includes increasing a flow of a coolant through the firstbattery pack relative to the flow of coolant through the second batterypack.
 4. The method of claim 3, wherein increasing the flow of a coolantincludes redirecting the flow of coolant from the second battery pack tothe first battery pack.
 5. The method of claim 1, further includingdisplaying messages regarding the detected thermal event on a displaydevice of the electric vehicle, the messages including at least one of alocation of the detected thermal event, or instructions to exit theelectric vehicle.
 6. The method of claim 1, wherein at least partiallypowering down the electric vehicle includes turning off substantiallyall power from the battery system after a predetermined amount of timeafter detecting the thermal event.
 7. The method of claim 1, whereindetecting a thermal event includes detecting the thermal event based onsignals from one or more sensors located in the first battery pack. 8.The method of claim 1, wherein detecting a thermal event includesdetecting the thermal event based on signals from a pressure sensorlocated in the first battery pack.
 9. The method of claim 1, whereindetecting a thermal event includes detecting the thermal event based onsignals from a humidity sensor located in the first battery pack.
 10. Amethod of controlling the battery system of an electric vehicle, thebattery system including a plurality of battery packs, each battery packincluding multiple battery cells electrically coupled together,comprising: receiving, at an electronic controller, data from one ormore sensors coupled to each battery pack of the plurality of batterypacks; detecting, based on the received data, a thermal event in a firstbattery pack of the plurality battery packs; electrically decoupling thefirst battery pack from the battery system in response to the detecting;and increasing a rate of cooling of the first battery pack relative tothe rate of cooling of a second battery pack of the battery system inresponse to the detecting.
 11. The method of claim 10, further includingturning off substantially all power from the battery system after apredetermined amount of time after detecting the thermal event.
 12. Themethod of claim 10, further including sending information to an operatorof the electric vehicle in response to the detecting, the informationincluding instructions to evacuate the vehicle using an indicated exitof the electric vehicle.
 13. The method of claim 10, further includingwirelessly sending information regarding the detected thermal event to alocation remote from the electric vehicle in response to the detecting.14. The method of claim 10, wherein the receiving data includesreceiving data indicative of a gas being released from one or morebattery cells of the first battery pack.
 15. The method of claim 10,wherein increasing a rate of cooling includes redirecting a flow of acoolant from the second battery pack to the first battery pack.
 16. Amethod of controlling the battery system of an electric bus, the batterysystem including a plurality of battery packs, each battery packincluding multiple battery cells electrically coupled together,comprising: detecting, based on data received from one or more sensorscoupled to each battery pack of the plurality of battery packs, athermal event in a first battery pack of the plurality of battery packs;sending information regarding the detected thermal event to an operatorof the electric bus; turning off substantially all power from thebattery system after a predetermined amount of time after detecting thethermal event; and increasing a rate of cooling of the first batterypack relative to the rate of cooling of a second battery pack of theplurality of battery packs in response to the detecting.
 17. The methodof claim 16, wherein the detecting includes detecting a thermal eventbased on data indicative of a gas being released from at least onebattery cell of the multiple battery cells in the first battery pack.18. The method of claim 17, further including receiving data indicativeof a gas being released from at least one of (a) a pressure sensor, and(b) a humidity sensor.
 19. The method of claim 16, wherein turning offsubstantially all power from the battery system includes sequentiallyturning off power to different systems of the bus at different times.20. The method of claim 16, wherein increasing a rate of coolingincludes redirecting a flow of a coolant from the second battery pack tothe first battery pack.